Among isothiazoline compounds, in the past 2-methyl-4-isothiazoline-3-one (hereinafter, sometimes this is simply referred to as MIT) and 5-chloro-2-methyl-4-isothiazoline-3-one (hereinafter, sometimes this is simply referred to as Cl-MIT) have been used as an antiseptic agent, a bactericide, and an antibacterial agent. In water treatment, too, it has been known that these compounds are excellent in an antibacterial activity to microorganisms included in water, and also have an effect to suppress adhesion of a biofilm; and thus, various proposals have been made with regard to the use of the isothiazoline compound as an antibacterial agent (bactericide), etc.
For example, in PTL 1, an antibacterial composition including a composition formed of MIT, Cl-MIT, a stabilized hypochlorite salt, and a bromide is disclosed.
In PTL 2, it is described that when algae are generated in a cooling water system under an antibacterial treatment by using chlorosulfamic acid and/or a salt thereof, an isothiazolone compound (isothiazoline compound) is added therein.